South Korea says it has seen indications that North Korea is preparing more missile launches, possibly an intercontinental ballistic missile (ICBM), after Pyongyang conducted its sixth nuclear test.

The Defense Ministry said on September 4 that it was strengthening its U.S.-made THAAD missile-defense system, whose deployment south of Seoul has been strongly opposed by China and Russia.

It said it would soon temporarily deploy four more launchers of the system to join the two already at the site in Seongju.

The ministry said the United States would seek to deploy a nuclear-powered aircraft carrier to seas off the Korean Peninsula.

There will also be more live-fire drills this month, involving Taurus air-to-surface missiles mounted on F-15 jets, it added.

Earlier on September 4, South Korea carried out live-fire exercises simulating an attack on the nuclear site where the North carried out its test, with both ground- and air-launched rockets.

Pyongyang announced on September 3 that it successfully tested what it said was a hydrogen bomb capable of being loaded on a long-range missile in what appeared to be North Korea’s most powerful nuclear test.

Seoul estimates its strength at 50 kilotons -- five times the size of the North's previous nuclear test in September 2016 and more than three times bigger than the U.S. device that was dropped on Hiroshima in 1945.

Show Of Unity

In a rare show of unity, the international community strongly condemned the latest nuclear test, with China urging the secretive communist state to stop "wrong" actions and Russia saying it could lead to "serious consequences."

The UN Security Council is to hold an emergency meeting later on September 4 to discuss its response to the test.

The secretary of Russian President Vladimir Putin's Security Council, Nikolai Patrushev, arrived in Seoul for talks on security issues.

North Korea’s nuclear and ballistic-missile program are banned by United Nations resolutions, but Pyongyang has continued to carry out tests in defiance of UN sanctions and international pressure.

In July, it test-launched two ICBM-class missiles and threatened to fire missiles toward the U.S. Pacific territory of Guam.

The Security Council last imposed sanctions in August, targeting North Korean exports.

Ahead of the council meeting, South Korea and Japan's leaders agreed to pursue stronger UN sanctions against Pyongyang, said a South Korean presidential palace spokesman.

In a phone call with Japanese Prime Minister Shinzo Abe on September 3, U.S. President Donald Trump said his country was prepared to defend itself and allies "using the full range of diplomatic, conventional, and nuclear capabilities," the White House said.

It followed remarks by U.S. Secretary of Defense Jim Mattis that any threats to the United States would be "met with a massive military response" and that North Korea risked "total annihilation" with its actions.

Meanwhile, both Russia and China, Pyongyang's main economic backer, reiterated on September 4 that any solution to the crisis could only come through talks.

China's Foreign Ministry said on September 4 that it had lodged a diplomatic protest with North Korea over the test.

North Korea is clear about China's opposition to its tests, a ministry spokesman said, adding that Beijing upholds talks as the means to resolve the issue.

It also warned North Korea against proceeding with its reported plans to launch another ballistic missile, saying the Security Council resolutions prohibit such activities.

Foreign Ministry spokesman Geng Shuang also criticized U.S. President Donald Trump's comment about the United States considering stopping trade with countries that do business with North Korea.

"It is unacceptable that, on the one hand, it is hard to make efforts to resolve the North Korea nuclear issue and on the other hand, [China's] own interests are subject to sanctions or damage, which is neither objective nor fair," he said.

Russian Deputy Foreign Minister Sergei Ryabkov also called for restraint, saying, "Any clumsy step could lead to an explosion.”

Ryabkov also told reporters at a BRICS summit in China that Moscow would need to react to the expansion of the THAAD antimissile system in South Korea.

"It inevitably will raise the question about our reaction, about our military balances," he said.